Welding and cutting of plastics film or foil is particularly important with flexible packaging equipment, for example in the bag making industry, and also in form/fill/seal machinery.
There are three main methods for welding plastics film or foil utilised in packaging machinery. These are hot metal welding, radio frequency welding and ultrasonic welding.
All three of these methods have the disadvantage of requiring mechanical contact between the substrate to be welded and the cutting equipment. Mechanical contact can result in substrate sticking to the sealing/cutting equipment, and requires blades or the like which need regular sharpening, replacement, cleaning and maintenance. These known methods and apparatus are also mechanically complex.
Furthermore, machinery employing these methods requires a stop/start cycle, the stop component necessary to allow time for the mechanical contact between the welding head and the substrate to produce the required weld. Alternatively, the welding head may move with the substrate, but this requires multiple welding heads in order to achieve an acceptable processing speed. The requirement for multiple welding heads further adds to the mechanical complexity of the equipment.
Another difficulty associated with existing equipment employing welding heads is that some plastics materials are difficult to seal, and it may be impractical to weld thick gauge substrates, to weld plastic to metal foil, or to weld temperature-resistant materials.
Moreover, with hot metal, radio frequency and ultrasonic welding the focusing of heat may be poorly controlled making it difficult to weld or seal shrink film, for example. In addition, these conventional systems may require ramping in of dwell time and preheating of sealing mechanisms which add to their complexity. If they don't have such features then there are inefficiencies associated with scrap substrate.
Lasers are employed in the packaging industry in various capacities, including for producing score lines on plastics packaging material to facilitate opening of such packaging, and for cutting out and welding customised shapes of bags made of fluorocarbon materials. However, where such laser technology has been employed it has not generally been adapted for use in association with highspeed packaging machinery, In particular, the laser beams have been fixed, for the production of welds, seals or score lines in a longitudinal direction along a moving film, or means of lateral scanning have been inefficient, of limited lateral span and/or not designed for use with continuously moving webs or films of material.
Thus, it is an object of the present invention to provide a method and apparatus for welding and/or cutting flexible packaging material in motion, employing lasers which overcomes or reduces the above-mentioned problems, or which at least provides the public with a useful alternative.
Other objects of the present invention may become apparent from the following description which is given by way of example only.